Atmospheric CO₂

Time to look more to the present.  CO₂ is a relatively regular feature in the news and something we all often hear discussed in various situations.  With this in mind I found a rather interesting paper by Lacis et al (2010) in Science titled “Atmospheric CO₂: Principal Control Knob Governing Earth’s Temperature” (Lacis et al, 2010).  The paper opens with a nice little introduction explaining to the reader that CO₂ “does not condense and precipitate from the atmosphere at current climate temperatures” (Lacis et al, 2010).  CO₂ along with other noncondensing greenhouse gases such as ozone, N2O, CH4, and chlorofluorocarbons prevent a collapse of the greenhouse effect due to their radiative forcing effects and account for 25% of the greenhouse effect (Lacis et al, 2010).  Its true’ to say that they are a necessity of life, without the greenhouse effect the planet would become icebound.  But as with most things in life, it’s about just the right balance, too much of a good thing is never good in the long term.  The paper goes on to say the remaining 75% of the greenhouse effect is provided by water vapour and cloud due to feedback processes. 

“It often is stated that water vapour is the chief greenhouse gas (GHG) in the atmosphere. For example, it has been asserted that about 98% of the natural greenhouse effect is due to water vapour and stratiform clouds with CO₂ contributing less than 2%.  If true, this would imply that changes in atmospheric CO₂ are not important influences on the natural greenhouse capacity of Earth, and that the continuing increase in CO₂ due to human activity is therefore not relevant to climate change.”  (Lacis et al, 2010). 

 

However Lacis et al (2010) go on to explain that whilst the strongest climate feedbacks are resulted from water vapour in radiative forcing experiments global climate change forcing is not as a result of this.  Their study found CO₂ to be the principle controlling atmospheric gas with respects to controlling the greenhouse effect.  (Are you shocked by this?  I doubt it somehow.)  In relation to our current climate they note that solar irradiance has only negligible impacts.  At the time of publishing in 2010 the current CO₂ level stood at 390 ppm, but an interglacial maximum’s typical levels would be approximately 280 ppm.  CO₂ has a very long residence time of thousands of years, Lacis et al (2010) express their concern at ever increasing levels due to anthropogenic activity by stating “the atmospheric CO₂ control knob is now being turned faster than at any time in the geological record.” (Lacis et al, 2010)

 

NASA (2010). How Carbon Dioxide Controls Earth's Temperature [online]. Available from: <http://www.giss.nasa.gov/research/news/20101014/>. [Accessed 08th January 2016].

Reference;

Lacis, A.A. Schmidt, G.A. Rind, D. Ruedy, R.A. (2010). Atmospheric CO₂: Principal Control Knob Governing Earth’s Temperature. Science. 330, pp.356-359.